Strengths: I bought the 860's as the 768 model was discontinued. I found them fine except for the heels which rapidly wore down in a very short period. My weight, running technique nor routes have varied much so I can only suggest a softer compound. I own several pairs of 768's and have used them for my marathon training with no excessive heel wear despite having clocked up several hundred miles.
Weaknesses: No "Cons" just disappointed in the heel wear.